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Because frankly, I don't this ad would appeal to most of my users. It's kind of related but not really. For example (this example is totally fictional), let's say you had a site about Superman and the advertiser was selling refrigerators with a Superman logo on it. It's kinda like "huh?"
However, at this point there is simply no way of knowing if people click through an ad like this or not, right? I guess I could block that advertiser and see if my stats improve.
I think the only reason you see that ads more frequently is because its bid is high enough to make itself show up among the keywords related to your pages.
If you do not like it, filter it a couple of days and observe the stats to see if they would change much.
but if the bid is higher than revenues from clicking it are also higher for us pubslihers! so better not to remove it!